How to Calculate Your Target Heart Rate Using The Karvonen Formula

Smartwatch showing pulse.
Smartwatch showing pulse. Guido Mieth / Getty Images

When it comes to exercise and weight loss, one of the most important elements to pay attention to is your intensity.  How hard you work determines how many calories you burn, how quickly you build endurance, and whether you're getting the absolute most out of your exercise time.

Experts have figured out an ideal range of heart rates that allow you to work as hard as you need to without overdoing it or, on the other hand, wasting time by not working as hard as you could.

These target heart rate zones give you a starting point for figuring out just how hard you need to work when you exercise. So, how do you figure out your target heart rate zones?

One way to do that is by using The Karvonen Formula, a mathematical formula that helps you determine your target heart rate zone.

The formula involves using your maximum heart rate (MHR) minus your age to come up with a target heart rate range. This ends up as a percentage of your MHR, which allows you to figure out how high or low your heart rate should be.

Staying within this range will help you work most effectively during your cardio workouts.

What You Should Know About the Karvonen Formula

The Karvonen Formula is one of the most popular calculations used for figuring out heart rate zones, but there are a couple of issues that have come to light in recent years.

First, the old formula used the number 220 as an average maximum heart rate which, research has shown, is just plain wrong.

It t doesn't take into account the differences in heart size and heart rates that exist in all of us.

In fact, it's been shown to regularly underestimate heart rate zones for 90% of people studied. That means, using 220 in the formula will usually give you lower heart rate zones than you really need to work at the right intensity.

In recent years, scientists have tried to correct for this number and have come up with a different Maximum Heart Rate that is 206.9. This still won't fit every single person, but it may give you numbers that are a bit closer to reality.

Another issue with the Karvonen Formula is that research has found that women have a different heart rate response to exercise. This once again changes the formula for women. In this case, it becomes  206 - (.88 x age) = MHR instead of 206.9

To see how all this works in the real world real world, below are two examples that use the  Karvonen Formula to calculate heart rate zones. Besides the numbers mentioned in the formula, you'll also need to know your resting heart rate. To find this, take your pulse for one full minute when you first wake up in the morning.

If you can't do that, try taking your pulse after resting for 30 minutes or so. You can also use a heart rate monitor to track your heart rate as well. 

For the first example, take a 23-year-old man with a resting heart rate of 65 beats per minute. This formula also includes an updated calculation of maximum heart rate, which is 206.9 instead of 220.

Using this calculation, we can figure out the low end of this person's target heart rate zone as well as the high end.

The low end is considered about 65% of MHR, while the high end is considered about 85% of MHR and you'll see both of those percentages used in the examples.

The Karvonen Formula for a Man

Start with the following formula:

206.9 - (0.67 x 23 (age)) = 191
191 - 65 (resting heart rate-RHR) = 126
126 * 65% (low end of heart rate zone) OR 85% (the high end) = 82 OR 107
82 + 65 (resting heart rate) = 147
107 + 65 (rhr) = 172
The target heart rate zone for this person would be 147 to 172 beats per minute. Remember, this is only an estimate and may have to be tweaked during workouts.

The Karvonen Formula for a Woman

For the next scenario take a 49-year-old woman with a resting heart rate (RHR) of 65.

Remember, for women the MHR changes to 206 - (.88 x age):

206 - (.88 x 49) = 163163 - 65 (RHR) = 98
98 * 65% (low end of heart rate zone) OR 85% (high end) = 64 (65%) or 83 (85%)
64 + 65 (RHR) = 129
83 + 65 (RHR) = 148
The target heart rate zone for this person would be 129-148 beats per minute.

If math isn't your thing, there are plenty of online calculators you can use, such as this Target Heart Rate Calculator

Keep in mind that this calculation relies on the old 220-age formula, which can be wrong by as much as 12 beats, so you should use the results as a guideline and adjust your heart rate to match your Perceived Exertion. That means, however hard you're working, try to match it to a number between 1 and 10 as to how hard that activity feels.

For example, if you're warming up, your perceived exertion might be around a 3 or 4, a comfortable pace. If you're feeling slightly breathless but you can still talk, that might be a moderate pace, around a Level 5 or 6.

Monitoring Your Heart Rate

Once you get your heart rate, how do you monitor it?  The easiest way is to use a Heart Rate Monitor. There is a huge variety of heart rate monitors out there, some as simple as just giving your heart rate and others with extras such as GPS or the ability to track your sleep. 

Two great options:

  1. The Apple Watch - You can actually get your heart rate without having to wear a chest strap and the watch tracks your activity throughout the day, allowing you to record workouts, keep track of how many steps you've taken and even reminding you to stand up if you've been sitting too long.  It also lets you control your music on your iPhone, which is a must for outdoor workouts.  You never even have to take out your phone, which is handy.
  2. The FitBit Charge - This is another option for tracking your heart rate without a chest strap and it's much cheaper than the Apple Watch.  You can track all the important things, steps, distance, and calories burned along with your heart rate, which makes the calories burned more accurate.  This can also be used to monitor your sleep every night, although the watch itself is a little bulky.

Of course, you don't need a heart rate monitor, but it really does help to see the numbers in black and white. That gives you an objective measure of how hard you're actually working, which can make your workouts better over time.

The more you understand how your body responds to different types of exercise, the more you can control how those workouts can work for you.

Sources:

Tanaka H, Monahan KD, Seals DR. Age-predicted maximal heart rate revisited. J Am Coll Cardiol. 2001 Jan;37(1):153-6.

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